[neverdem]

Cold ocean waters (particularly where the wind blows hard) absorb CO2 from the atmosphere. Warm waters where the wind doesn't blow hard release it.

So in the tropics where ocean acidification is hypothesized as the cause of coral reef degradation is not the effect of atmospheric CO2 due to human activity. That ocean water is releasing CO2 absorbed ages ago. It shifts your equation to the left. The surface waters in the tropics release CO2.

CO2 + H2O <----> H2CO3 (carbonic acid) <----> H+ + HCO3-

[cogitator]

Well, acidification anywhere in the oceans is a result of human activity, because the increased absorption is due to increasing atmospheric concentrations. But the tropics are less affected, because you get the most effect where the absorption is strongest. Warm waters with light winds = least effect.

Change in sea surface pH caused by anthropogenic CO2 emissions between the 1700s and 1990s.